Narrated by Nafi': Whenever Ibn 'Umar started the prayer with Takbeer, he used to raise his hands. Whenever he bowed, he used to raise his hands (before bowing) and also used to raise his hands on saying, "Sami' Allaahu Liman Hamida", and he used to do the same on rising from the second Rak'a (for the 3rd Rak'a). Ibn 'Umar said: "The Prophet used to do the same." [Bukhaaree, The Book of The Characteristics of the Prayer]

In his Saheeh, Imam Muslim included a chapter: The Desirability of Raising The Hands Opposite The Shoulders at the Time Of Beginning The Prayer and at the Time of Bowing and at the Time of Returning to the Erect Position after Bowing. In this chapter are six ahadeeth, narrated by various companions.

"Whoever prohibits people from raising their hands during the prayer (at the start of the prayer, before ruku', and after ruku') is an Innovator!

Quote:

'Abdullaah Ibn 'Umar (radiallaahu 'ahumma) would gather pebbles to throw at whoever he saw not raising his hands during the prayer - to show his rejection of them - because they opposed the Sunnah of Muhammad (salallaahu 'alayhi wa sallam)."